The state of the art includes various aspiration and plugging systems for melting volumes, performed by means of adjacent cooling pipes through which water flows, or by means of walls formed by sheet metal cooled by sprayed water, or again by means of refractory materials able to resist high temperatures.
The gases produced during the melting process are aspirated by means of a pipe and an aperture made in the roof of the furnace itself, commonly known as the fourth hole.
In existing systems, it has been noticed that with the direct aspiration of the fumes huge quantities of solid particles are transported into the plant; these particles increase the consumption of electric energy of the auxiliary equipment, such as the fans, used for the aspiration of the particles, and limit the duration of the filters through which the fumes pass. Above all, since a large part of the particles transported by the fumes consists of metallic material, this also reduces the productivity of the furnace. In addition, when the material loaded is fine material, such as for example DRI (directly reduced iron) or IC (iron carbide, or material obtained from the reduction of iron material containing a high percentage of Fe.sub.3 C), the yields are further diminished.